I. Field of the Invention
The present invention relates generally to welding and, more particularly, to a resistance welding tip assembly.
II. Description of the Prior Art
Resistant welding machines typically comprise a welding jaw having two spaced apart welding tips that are movable relative to each other. During the welding operation, the welding tips are moved together thus sandwiching the work to be welded in between the tips. Pneumatic, hydraulic or electrical actuators are commonly used to create a clamping jaw force between the welding tips and thus on the work.
During a welding operation, a high amperage power source is applied to the welding tips so that the current flows through the welding tips and thus through the workpiece sandwiched in between the welding tips. In doing so, the workpiece becomes heated thus liquefying the workpiece in the area between the welding tips in the desired fashion. Upon cooling, the weld solidifies thus completing the welding operation.
In order to obtain an adequate weld, it is necessary to maintain a relatively high current density between the welding tips during the welding operation. Unless such high current density is obtained during the weld, insufficient melting of the workpiece results and, in turn, results in an inadequate weld. Such inadequate welds are prone to failure in use.
Ideally only the workpiece would melt during the welding operation so that the current density between the welding tips would remain substantially constant during sequential welds. Unfortunately, however, during a welding operation the welding tips themselves become soft from the welding heat and tend to mushroom during the welding operation. The mushrooming of the welding tips increases in magnitude over a series of sequential welds and also increases with increased pressure applied to the welding tips during the welding operation.
As the welding tips mushroom, the effective area of contact between the welding tips and the work also effectively increases. This, in turn, decreases the current density through the workpiece during a welding operation and can result in inadequate welds.
In order to avoid unsatisfactory welds, it has been the previous practice in manufacturing facilities to periodically replace the welding tips after a preset number of welding operations. For example, if the welding tips can be used for 200 welding operations without suffering excessive mushrooming of the type which would result in inadequate welds, the welding tips would be automatically replaced after 200 welds. This previously known procedure, while adequate to prevent unsatisfactory welds, suffers from its own disadvantages.
First, the periodic replacement of the welding tips after a predetermined number of welds results in a shutdown of the manufacturing assembly line for the period of time necessary to replace the welding tips. A still further disadvantage is that the periodic replacement of the welding tips adds to the overall manufacturing cost due to the replace cost of the welding tips themselves.